Along with the development of the display manufacturing technologies, thin film transistor liquid crystal displays (TFT-LCDs) have been prevailing in the recent flat display market due to characteristics, such as compactness, low power consumption, and non radiation, and the like.
A prior art process for producing a TFT array substrate commonly comprises: depositing a gate metal film, a gate insulating film, a metal oxide film (semiconductor film), a source-drain metal film, a passivation layer film as well as a transparent conductive film onto a substrate, and forming successively, through several photolithography processes, the patterns of a gate electrode, a gate insulating layer, a semiconductor layer, a source electrode, a drain electrode, a passivation layer as well as a transparent pixel electrode. Usually, one photolithography process successively comprises film formation, exposure, development, etching and removing etc.; the etching process comprises dry etching and wet etching. Wet etching has the drawbacks of poor anisotropy, severe undercutting, poor control on patterns, failure for fine characteristic dimensions, production of considerable chemical liquid waste, and the like; in contrast, due to the advantages, such as good anisotropy, good controllability, flexibility, repeatability, processing safety, easy automation, no chemical liquid waste, no contamination introduced during process, and high brilliancy, and the like, dry etching is widely used in the photolithography process for a TFT array substrate.
In the above processes for making a TFT array substrate, the formation of the semiconductor layer and the source electrode as well as the drain electrode is conducted through successive processes, that is, the semiconductor layer film is firstly deposited and then the source-drain metal film are deposited. In order to prevent the damages to the semiconductor film in depositing the source-drain metal film, typically one etching stop layer is deposited onto the semiconductor film, and next the source-drain metal film is deposited. After the patterning process, the etching stop layer retains within the channel between the source electrode and the drain electrode over the semiconductor layer. One surface of the semiconductor layer contacts the etching stop layer, and the other surface contacts the gate insulating layer. The etching stop layer and the gate insulating layer are usually formed of an insulating material, such as SiNx, Al2O3, SiOx, etc. If the semiconductor layer is formed of a metal oxide material and the etching stop layer and the gate insulating layer are formed of SiNx, SiNx contained in the etching stop layer and the gate insulating layer will seize the oxyanion in the metal oxide of the semiconductor layer, causing de-oxygen of the metal oxide of the semiconductor layer and thus unstable behavior of the TFT array substrate.
In order to enhance the stability of the TFT array substrate, the etching stop layer and the gate insulating layer may also be formed of Al2O3 or SiOx. However, in the case of dry etching, if the patterns of the etching stop layer and the gate insulating layer are formed of Al2O3 or SiOx, the etching rate will be low, which is adverse to large scale production.